1. Field of Invention
The present invention relates generally to methods and apparatus for use in welding panel boards and tubing to header pipes. More particularly, the present invention relates to methods and apparatus for welding solar panel boards and thermal heat exchanger tubing to header pipes.
2. Background
As the efficient use of energy becomes more of a concern, the use of solar energy heating systems is becoming increasingly popular. The use of thermal energy storage (TES) systems, in particular, is becoming more prevalent. TES systems enable lower cost energy, e.g., electricity during off-peak demand hours, to be used, for example, to freeze ice which may be melted during peak hours to thereby provide cooling capabilities without significant usage of electricity during peak demand hours.
Heating systems which use solar energy are typically arranged to capture solar heat and to store the solar heat until the heat is needed. One particularly efficient solar heating system captures solar heat for use in heating swimming pools. FIG. 1a is a diagrammatic representation of a solar heating panel which is suitable for use in heating a swimming pool. Solar heat is captured by solar heating panel 102 using an array of heat exchange tubes 104 which are preferably made of a dark, thermoplastic material. Heat exchange tubes 104 are oriented such that heat exchanges tubes 104, as for example heat exchange tubes 104a and 104b, are adjacent to each other. Further, adjacent heat exchange tubes 104 are "attached" such that heat exchange tubes 104 form a panel board 108, as shown.
Water generally runs through header pipes 110, which are made of a thermoplastic material, and heat exchange tubes 104. The water is typically warmed as it passes through heat exchange tubes 104. That is, solar heat that is captured by heat exchange tubes 104 is used to warm water as water flows through heat exchange tubes 104. As shown, caps 112 are included at the ends of header pipe 110 for interconnection purposes. Caps 112 are often fabricated from a material which prevents creep from occurring in header pipe 110. Through caps 112, a pump or other water supply mechanism is generally coupled to header pipe 110 to enable water to be run through heat exchange tubes 104. Additional solar heating panels 102 may be connected together, effectively in parallel, in order to form larger solar heating systems.
TES systems are typically arranged to use electricity at off-peak energy demand periods to "store" energy for use at a later time, as mentioned above. That is, electricity is used when the cost of electricity is lower to produce and store energy which may be used when the cost of electricity is higher. Heat exchangers are generally included as a part of a TES system. In particular, cooling liquid, e.g., a glycol solution, may be pumped through a heat exchanger to store energy in a thermal energy storage medium, which is typically in the form of either a low-temperature fluid or a solid such as ice, and is in contact with the heat exchanger. Then, at a later time, glycol solution is pumped through heat exchangers in the thermal energy storage medium to produce chilled air for cooling purposes, as will be appreciated by those skilled in the art. For example, the chilled air may be used as a part of an air-conditioning system that is arranged to cool a building.
FIG. 1b is a diagrammatic representation of heat exchanger that may be part of a TES system. Like the solar heating system described above with respect to FIG. 1a, heat exchanger 120 includes header pipes 124 and heat exchange tubes 128. Heat exchange tubes 128 are arranged in an array such that heat exchange tubes 128 are substantially parallel and adjacent to one another. Within heat exchanger 120, distal ends of heat exchange tubes 128 are attached to header pipes 124. In general, heat exchange tubes 128 are made of a dark, thermoplastic material. Caps 130 are generally attached to the ends of header pipes 124 to permit connections between multiple header pipes, and to prevent creep in header pipes 124, as mentioned above. Caps 130 may also be configured to facilitate the coupling of header pipes 124 with a pump or similar supply mechanism which allows cooling fluid to be pumped through header pipes 124 and heat exchange tubes 128.
Coupling heat exchange tubes to header pipes typically involves a combination of welding and melting processes. In general, a panel board, i.e., an array of adjacently connected heat exchange tubes, is welded directly to a header pipe, or pretreated to create a flange surface which may be used to attach the panel board to a header pipe. FIG. 2a is a diagrammatic representation of a portion of a panel board prior to the formation of a flange. A panel board 202 includes a plurality of tubes 204, which are generally thermoplastic tubes. Tubes 204 include openings 208 which pass through ends 212 of tubes 204. In other words, tubes 204 are not sealed at ends 212.
Ends 212 are typically pretreated to melt tubes 204 in the vicinity of ends 212. This pretreatment of ends 212 often involves heating ends 212, e.g., using hot air, and forming the required flange in a mold, typically by cooling ends 212 in the mold. As such, creating a surface which may be coupled to a header pipe generally involves separate pretreatment and cooling processes. Alternatively, a single die, which is first heated for the pretreatment, then cooled to create the flange surface from pretreated ends 212, may be used.
FIG. 2b is a diagrammatic representation of panel board 202 of FIG. 2b after ends 212 have been pretreated and formed in a mold. As will be appreciated by those skilled in the art, machinery that is used to create a flange at the end of a panel board of thermoplastic tubes typically requires significant adjustments when the width of the panel board changes. By way of example, when the width of the panel board is to be changed, a thermoforming die that is specific for the width of the panel board must be installed in the machinery. Maintaining a full complement of thermoforming dies to accommodate different widths of panel boards is expensive, while having to make significant adjustments to machinery each time a different panel board width is to be used is inefficient.
A flange 220 is created at pretreated ends 212 from melted material, i.e., the thermoplastic material at and in the vicinity of the original ends of panel board 202, as shown in FIG. 2a. In general, a significant amount of material must be melted in order to create flange 220. Flange 220 is arranged to be sealed against a header pipe to form, for example, either a solar panel board or a heat exchanger. The creation of flange 220, however, may result in tubes 204 being substantially sealed or "pinched off." In other words, flange 220 may substantially block off tubes 204 such that openings 208' are significantly smaller than the openings in tubes 204 prior to the formation of flange 220. Often, openings 208' are essentially non-existent.
Alternatively, pretreated ends 212 may be welded directly to header pipe 248. When pretreated ends 212 may be welded directly to header pipe 248, tubes 204 are plugged by the wall of header pipe 248. As such, each tube must be drilled open in order to accommodate fluid flow.
With openings 208' either being non-existent or of a significantly smaller size than desired, openings 208' must be enlarged in order to permit fluid to flow through tubes 204 without a significant drop in pressure once a solar panel board or a heat exchanger is created from panel board 202. Therefore, openings 208' are enlarged or, in some cases, created, by any process which essentially removes material from flange 220 in the areas where openings 208' are desired. Such processes are typically time-consuming, and generally include the use of pin-like shafts which are heated and are arranged to push through thermoplastic material. Other processes may include drilling process used to drill through thermoplastic material. The processes used to enlarge openings 208' through flange 220 may also cause debris, e.g., the material which was obstructing openings 208', to enter tubes 204.
Once openings 208' of an acceptable size are created, panel board 202 is considered to be ready to be coupled to a header pipe. FIG. 2c is a diagrammatic representation of a header pipe and the panel board of FIG. 2b, with properly sized openings, which is arranged to be coupled to the header pipe. A header pipe 248 includes flow openings 250 which are arranged to be aligned with a sub-header channel 260, or sub-header, which distributes flow to each opening 208". Once openings 250 are suitably aligned with openings 208", then flange 220 and at least the portion of header pipe 248 that will be coupled to flange 220 are heated. Typically, header pipe 248 and flange 220 are heated to their respective melting point temperatures. Such heating is often performed using an infrared heat source, or a heated platen. Once the melt point temperatures are reached, header pipe 248 and flange 220 are often pressed together. Alternatively, panel board 202 and header pipe 248 may be welded after heating. The welding after heating may occur without flange 220, in which case openings 208" and 250 must effectively be aligned.
After panel board 202 and header pipe 248 are assembled, other processes associated with the fabrication of a solar heating system or a heat exchanger are also typically performed. By way of example, caps are often added to the ends of the header pipes to prevent creep from occurring in the header pipes and to allow multiple panel boards to be coupled together. Also, in order to create a heat exchanger like the heat exchanger described above with respect to FIG. 1b, after a panel board is assembled to header pipes, the tubes in the panel board must be manually separated. Although having to manually separate tubes is time-consuming and, hence, inefficient, the above described processes used to couple header pipes with the flange and panel boards may not be readily used to couple a series of individual tubes to header pipes. Flanges created on individual tubes often leak, and are both difficult to handle and difficult to align.
As demand for solar heating systems and TES systems increases, reducing the number of process steps associated with the fabrication of such systems would increase the production of such systems. For example, reducing the number of process steps associated with coupling panel boards to header pipes would enable the efficiency of the overall fabrication process to be increased. Further, allowing process steps to be readily adapted to panel boards of different sizes would also increase the efficiency with which the fabrication process may occur. In addition, eliminating inefficient processes would reduce the overall costs associated with producing solar heating systems and TES systems. Therefore, what is desired are methods and apparatus for efficiently coupling header pipes to heat exchange tubes.